This invention relates to a manufacturing method of a semiconductor device, in particular, a manufacturing method effective for forming multilayer interconnects, wherein an insulating film having a low resistance against oxygen plasma is used as an interlayer dielectric.
In accordance with the increase of the integration density of the LSI in recent years, the wiring layer of the LSI device has been decreased in size and increased in number. In addition to the downsizing and the multilayering of the wiring, the device with high performance is required to decrease the capacitance between the wirings when the device is formed fine in multilayered structure. In order to decrease the capacitance generated between the wirings, it is effective to use an interlayer dielectric having a low dielectric constant, for example.
As such an interlayer dielectric having low dielectric constant, an insulating film formed from siloxane and organic material have been proposed to be used instead of a silicon oxide film as the conventional interlayer dielectric. This type of an insulating film can be formed by the spin coating method, and thus is planarized without performing any planarization process such as the etch-back or the CMP (Chemical Mechanical Polishing). The multilayer structure can be therefore easily attained. In short, with use of such an interlayer dielectric, the reduction of the dielectric constant and the multilayering can be easily attained simultaneously.
The sectional views of the device according to the conventional method using an organosiloxane film as the low-dielectric constant interlayer dielectric are shown in FIGS. 1A, 1B, 1C, 1D, and 1E to explain each step of the manufacturing process.
As shown in FIG. 1A, a first metal layer 83 is formed above a silicon substrate 81 in which the element isolation and the element formation have been performed, so as to hold an insulating film 82 between itself and the substrate. An organosiloxane film 84 is then formed by the spin coating method on the insulating film 82 on which the first metal layer 83 is formed, as shown in FIG. 1A.
Next, as shown in FIG. 1B, a photoresist pattern 85 having an opening pattern above the first metal layer 83 is formed on the organosiloxane film 84.
The organosiloxane film 84 is then etched by the RIE method with use of the photoresist pattern 85 as a mask in order to form a contact hole reaching the first metal layer 83, as shown in FIG. 1C. The photoresist pattern 85 is removed with use of plasma thereafter (see FIG. 1D).
At last, a Ti/TiN barrier metal film 86 covering the sidewall and the bottom of the contact hole is formed as shown in FIG. 1E, and then a second metal layer 87 formed of Al added with Cu is formed by the sputtering to fill the contact hole. In this manner, a double-layered wiring structure is attained.
This wiring forming method, however, may cause the following problems:
The organosiloxane used as an insulating material having low dielectric constant has low resistance against oxygen plasma. Oxygen plasma used in the step shown in FIG. 1D to remove the photoresist pattern 85 thus may change the property of the organosiloxane film 84 to have high dielectric constant. The increase of the dielectric constant will increase the capacitance between the wirings, which may deteriorate the performance of the LSI device.
Further, the changed organosiloxane film 84 may corrode the first metal layer 83, the barrier metal film 86, and the second metal layer 87.
As one of effective methods of improving the resistance of an organosiloxane film against oxygen plasma, a surface treatment by oxygen ions has been known.
With use of this method, however, oxygen ions cannot reach the bottom of the contact hole since a contact hole of a fine LSI has a high aspect ratio, and thus the property of the side wall of the contact hole near the first wiring 83 cannot be completely improved.
If a too large amount of oxygen ions is deposited on the device in order that the oxygen ions can reach the bottom of the contact hole, the oxygen ions are implanted also into the first metal layer 83, thereby contact resistance between the first metal layer 83 and the second metal layer 87 will be increased.
In a dual damascene process wherein a contact hole and a wiring trench are simultaneously filled with a conductive film, the depth of the contact hole is increased by the depth of the wiring trench, and thus this problem caused by the improvement of the property of the surface of the film by the implantation of the oxygen ions will become more critical.
The above-mentioned problem will occur also in the case where an insulating film formed from organic material instead of siloxane is used as an interlayer dielectric having low dielectric constant.
As described above, it has been proposed in order to decrease the capacitance between the wirings to use an interlayer dielectric formed from siloxane or organic material having low dielectric constant.
Such a type of insulating film, however, has low resistance against oxygen plasma, and thus the property of the film may be changed by oxygen plasma used to remove the photoresist pattern formed thereon, to increase the dielectric constant of the film. The changed insulating film may corrode the metal layers formed near the interlayer dielectric.